How many pens of Insulin Glargine (insulin glargine) 100 units/mL solution are needed for a 90-day supply, given a nightly dosage of 30 units?

Insulin Glargine Pen Supply Calculation for 90-Day Prescription

Direct Answer

For a 90-day supply at 30 units nightly, dispense 9 pens with appropriate refills to ensure continuous coverage.

Calculation Methodology

Standard Pen Capacity

• Standard insulin glargine 100 units/mL pens contain 300 units per pen 1
• The FDA-approved insulin glargine SoloStar prefilled pen is a 3 mL single-patient-use device, delivering 300 total units 2

Mathematical Calculation

• Daily dose: 30 units
• Total units needed for 90 days: 30 units/day × 90 days = 2,700 units
• Number of pens required: 2,700 units ÷ 300 units/pen = 9 pens exactly

Practical Considerations for Dispensing

Account for insulin wastage:

• Pen priming before each injection uses small amounts of insulin 1
• Some insulin remains in the pen after the last full dose is administered 1
• Proper injection technique may result in minor losses 1

Buffer recommendation:

• While the mathematical calculation yields exactly 9 pens, prescribing 10 pens for a 90-day supply provides a safety buffer for the wastage factors mentioned above 1
• This approach ensures the patient does not run short before the refill date

Prescription Writing

For 90-day supply:

• Dispense: 9-10 pens (9 pens meets exact mathematical need; 10 pens provides practical buffer)
• Refills: 3 refills (to cover one full year of therapy)

Alternative approach for insurance coverage:

• Many insurance plans prefer 30-day supplies 1
• In this case: Dispense 3 pens monthly with 11 refills for annual coverage 1

Important Clinical Context

Insulin Delivery Method Selection

• Insulin pens are appropriate for patients requiring accurate insulin dosing, particularly those with dexterity issues or vision impairment 3
• Both insulin syringes and pens deliver insulin safely and effectively for achieving glycemic targets 3

Cost Considerations

• Insulin glargine follow-on products (like Basaglar) have lower costs with median NADAC of approximately $210 per 1,000 units for prefilled pens 3
• Original insulin glargine pens have median NADAC of approximately $272 per 1,000 units 3
• Medicare Part D has implemented a $35 monthly cap on insulin costs, which may affect out-of-pocket expenses 4